All was explained by the hand-written sign by S. Wilson, beneath the portrait in the TV Room: "No, this is not Prudence Risely. Amazing what you can do with meatloaf."
(Actually, the painting is "Georgia Laura White" by Olaf Martinus Brauner (1869-1947))
There is no known record of any image of Prudence; rather, the archivists who researched the Risley paintings in the early 70s saw her as an 18th-19th century frontier woman whose son, Russell Sage, made it big in the railroad business.
To your right, the front hall.